Saddle-shaped mitral valve annuloplasty prostheses with asymmetry, and related methods

ABSTRACT

A mitral valve annuloplasty prosthesis (ring or C) has a generally saddle shape, i.e., portions of the prosthesis that are or will be adjacent the anterior and posterior commissures of the valve are relatively low as compared to at least some other portions of the prosthesis that are or will be between the commissures. However, the saddle shape is asymmetrical, in that the portion that is or will be adjacent the posterior commissure is lower than the portion that is or will be adjacent the anterior commissure.

This application claims the benefit of U.S. provisional patentapplication No. 60/730,297, filed Oct. 26, 2005, which is herebyincorporated by reference herein in its entirety.

FIELD OF THE INVENTION

This invention relates generally to medical devices, and in particular,to annuloplasty rings and other similar prostheses for reshaping themitral valve annulus of a patient's heart. The invention also relates tomethods of using such prostheses.

BACKGROUND OF THE INVENTION

The mitral annulus represents the junction of the fibrous and musculartissue that joins the left atrium and the left ventricle. The mitralvalve is a bicuspid valve having a relatively large anterior leafletthat coapts or meets with a smaller posterior leaflet.

FIG. 1 illustrates a normal mitral heart valve 14 from the left atriumfrom a surgical view of the heart. The anterior portion A of the mitralannulus 15 forms a part of the “cardiac skeleton” and is bounded byanterior and posterior commissures 16, 17. The anterior commissure 16and posterior commissure 17 are generally at the junction points of theanterior leaflet 18 and the posterior leaflet 19. The junction pointsare also known as the anterolateral commissure 16 and posteromedialcommissure 17. The posterior portion P of the mitral annulus 15 consistsmainly of muscular tissue of the outer wall of the heart.

Referring to FIGS. 1 and 2, posterior leaflet 19 is divided into threescallops indicated as P1, P2, and P3 in sequence from the anteriorcommissure 16 counterclockwise to the posterior commissure 17. Anteriorleaflet 18 is also divided into three areas indicated as A1, A2, and A3in sequence from the anterior commissure 16 clockwise to the posteriorcommissure 17.

Ischemic heart disease can cause a mitral valve to become incompetent.In patients who suffer from cardiomyopathy due to ischemia, regions ofthe left ventricle lose their contractility and dilate. As the diseaseprogresses, the left ventricle enlarges and becomes more round in shape,going from a conical shape to more of a spherical shape. Referring toFIG. 2, papillary muscles 23, 25 are displaced down (inferiorly) andaway from each other. The change in the location of the papillarymuscles increases the distance between the papillary muscles and themitral valve annulus. This creates tension on the chordae tendonae 21that connect the posterior papillary muscle 23 to the mitral valveleaflets in the A2, A3, P2, and P3 regions of the annulus. Since thechordae tendonae 21 do not change their length significantly, thechordae 21 tend to pull or “tether” the mitral leaflets. In severe casesof left ventricle dilation, the tethering of the chordae prevents theleaflets from coming together or coapting correctly, resulting in mitralvalve regurgitation. In addition to remodeling of the left ventricle,the mitral valve tends to flatten during ventricular systole instead ofachieving its natural saddle shape. This also disrupts the naturalcoaptation of the mitral leaflets and the natural distribution ofstresses over the leaflets and chordae tendonae.

In ischemic mitral regurgitation (IMR), the entire circumference of themitral annulus may dilate. The posterior portion of the annulus maydilate more than the anterior portion because the anterior portion hasmore support from the heart's fibrous skeleton. In cases where IMR iscaused by posteromedial myocardial infarction, there may be anasymmetric dilation of the posteromedial annulus, which is indicated atA2, A3, P2, and P3. In this case, the IMR may be caused by tethering ofleaflet segments connected to the posteromedial papillary muscle. Thisis often in the A2, A3, P2, and P3 segments of the mitral valve.

Often, this type of mitral valve regurgitation is surgically repairedwith an annuloplasty ring (which may be either a complete ring or aC-shaped “ring” with an opening along the anterior side). The repairrestores proper leaflet coaptation by decreasing the diameter of themitral valve annulus, thereby mitigating the effect of the tethering ofthe chordae and the effects of dilation of the annulus. One surgicalcorrection for IMR is to tether the posteromedial annulus of the mitralvalve to the posteromedial papillary muscle. This papillary musclerelocation procedure reduces the chordal tension and allows the leafletsto coapt more effectively.

SUMMARY OF THE INVENTION

In accordance with the present invention, patient conditions like thosedescribed above are treated by applying an annuloplasty prosthesis (ringor C) that is shaped to push down the mitral valve annulus in thevicinity of the posterior commissure relative to other portions of theannulus. The prosthesis also dips down adjacent the anterior commissure,but it pushes down the portion of the annulus that is adjacent theposterior commissure farther than it dips down adjacent the anteriorcommissure. The effect of the prosthesis on the two commissure regionsof the annulus is therefore asymmetrical.

A mitral valve annuloplasty ring in accordance with the inventionincludes A1, A2, A3, P3, P2, and P1 segments connected to one another ina closed loop series in the order just mentioned. Each of these ringsegments is configured for placement adjacent the portion of a mitralvalve annulus that is adjacent the corresponding A1, A2, A3, P3, P2, orP1 segment of the mitral valve leaflets. The ring has ananterior-to-posterior (“AP”) axis that extends across the ring from itsanterior (A1/A2/A3) side to its posterior (P1/P2/P3) side. The AP axisis perpendicular to a line between two reference points that are spacedfrom one another along the anterior side of the ring. The AP axis alsobisects this line. These two reference points are located along theanterior side of the ring so that the AP axis also bisects a greatestwidth dimension of the ring, which greatest width dimension is measuredperpendicular to the AP axis. A third reference point is located alongthe posterior side of the ring to one side of the AP axis (e.g., theside that is toward or closer to the anterior commissure). Each of theabove-mentioned three reference points is spaced from the AP axis by 0.5mm. These three reference points lie in and thereby define a referenceplane. A point on the ring between the A1 and P1 segments, and anotherpoint on the ring between the A3 and P3 segments are both displaced fromthe reference plane to the same side of that plane. The amount ofdisplacement from the reference plane to the point between the A3 and P3segments is greater than the amount of displacement from the referenceplane to the point between the A1 and P1 segments.

Instead of being a complete ring as described above, an annuloplastyprosthesis in accordance with the invention may have a C shape. This Cshape can be similar to a complete ring in accordance with theinvention, but with a portion of the anterior side of the ring omitted.The gap in the C that results from this omission is generally locatedapproximately centrally on the anterior side of the C structure. Theanterior side of the C may be thought of as defining a trajectory thatincludes both the anterior structure (i.e., comparable to at leastportions of the A1 and A3 segments of a comparable ring) and a smoothcontinuation, across the gap, of both of those anterior structuralsegments. This trajectory follows a path through the gap that would beoccupied by material of the prosthesis if the C were instead a completering in accordance with the invention. The summary description providedabove for the various reference points and the reference plane of acomplete ring applies again to such a C, with the exception that thefirst and second reference points need to be described as being on theabove-mentioned trajectory because they may lie either in anteriormaterial of the prosthesis (if the gap is relatively small) or in thegap (if the gap is relatively large).

Further features of the invention, its nature and various advantages,will be more apparent from the accompanying drawings and the followingdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified or schematic view of a normal mitral heart valveas viewed from the left atrium during surgery.

FIG. 2 is a simplified or schematic view of mitral heart valvestructures that have been dissected vertically at the anterolateralcommissure and splayed open.

FIG. 3 is a simplified “plan” view of an illustrative embodiment of amitral valve annuloplasty ring in accordance with the invention. FIG. 3shows the ring having the same orientation as FIG. 1 shows a mitralvalve with which the ring may be used, but the scale of FIG. 3 is largerthan the scale of FIG. 1.

FIG. 4 is a simplified elevational view taken along the line 4-4 in FIG.3.

FIG. 5 is a simplified elevational view taken along the line 5-5 in FIG.3. The scale of FIG. 5 is larger than the scale of FIG. 3.

FIG. 6 is similar to FIG. 3, but shows an illustrative embodiment of aC-shaped mitral valve annuloplasty prosthesis in accordance with theinvention.

FIG. 7 is similar to FIG. 6, but shows another illustrative embodimentof a C-shaped mitral valve annuloplasty prosthesis in accordance withthe invention.

FIG. 8 is a view taken along the line 8-8 in FIG. 7.

DETAILED DESCRIPTION

An illustrative embodiment of a mitral valve annuloplasty ring 100, inaccordance with the invention, that is better suited to treating patientconditions like those described in the background section of thisspecification is shown in FIGS. 3-5. FIG. 3 shows ring 100 in the sameorientation as FIG. 1 shows a mitral valve to which ring 100 may beapplied. FIG. 3 shows that ring 100 has a generally D shape. Therelatively straight side of the D (toward the top in FIG. 3) is theanterior side of the ring in use. The curved side of the D (toward thebottom in FIG. 3) is the posterior side of the ring in use.

As shown in FIG. 3, ring 100 includes anterior segments A1, A2, and A3,and posterior segments P1, P2, and P3. Each of these segments isradially adjacent but beyond or outside the corresponding portion of themitral valve leaflets when the ring is in use (i.e., implanted in apatient adjacent the annulus of the patient's mitral valve). Thus, forexample, anterior ring segment A1 will be adjacent the base of the A1segment of anterior leaflet 18 when ring 100 is in use. Similarly,posterior ring segment P1 will be adjacent the base of the P1 segment ofposterior leaflet 19 when ring 100 is in use. The same correspondencebetween ring segments and leaflet segments applies to all ring segmentsall the way around ring 100. Thus it will be seen that ring 100 includesa closed loop series of segments A1, A2, A3, P3, P2, and P1, in thatorder.

In addition to defining ring segments as above, it is convenient torefer to several reference points on ring 100. Each of these referencepoints (A3/P3, A1/P1, R1, R2, and R3) is located on an axis that runsannularly around the ring and that passes coaxially through the centerof the core material of the ring. The point A3/P3 is the point at whichring segments A3 and P3 join or meet one another. This point is adjacentthe posterior commissure 17 (FIG. 1) of the mitral valve when ring 100is in use. (The exact location of point A3/P3 along the ring is notcritical. FIG. 3 thus tends to show the approximate locations of thevarious ring segments and points like A3/P3 and A1/P1. The locations ofthese features are, of course, generally as shown in FIG. 3.)

Another significant point on ring 100 is point A1/P1. This is the pointat which segments A1 and P1 join or meet one another. When ring 100 isin use, point A1/P1 is adjacent the anterior commissure 16 (FIG. 1) ofthe mitral valve.

Other points on ring 100 are reference points R1, R2, and R3. Thesereference points are located as will now be described. Ring 100 has aso-called anterior-posterior (“AP”) axis, which extends across the ringfrom its anterior side to its posterior side. The AP axis is located sothat it is perpendicular to and bisects a line between reference pointsR1 and R2. Reference points R1 and R2 are located along the anteriorside of the ring so that the AP axis bisects a greatest width dimensionW of the ring, which greatest width dimension is measured perpendicularto the AP axis. Anterior-side reference point R1 is spaced to one sideof the AP axis by 0.5 mm. Anterior-side reference point R2 is spaced tothe other side of the AP axis by 0.5 mm. Reference point R3 is on theposterior side of the ring and is spaced to one side (e.g., the R1 side)of the AP axis by 0.5 mm. Reference points R1-R3 lie in and therebydefine the location of a so-called reference plane.

(It should be noted that the “greatest width dimension” W is theperpendicular distance between two tangents to the ring that are bothparallel to the AP axis and that are as far apart as possible onopposite sides of the ring. It is possible that there may be somedistance across the ring, measured in some other way, that is greaterthan W, but that is irrelevant to the present invention and not what ismeant by the “greatest width dimension” as used herein.)

FIG. 4 shows that ring 100 is not planar. In the particular embodimentshown in FIGS. 3-5, each of anterior ring segments A1, A2, and A3 issubstantially out of sight behind the corresponding posterior ringsegment P1, P2, and P3 in FIG. 4. This is not necessarily exactly thecase in all embodiments, but it simplifies FIG. 4 and facilitates thepresent discussion. The reference plane referred to in the precedingparagraph is identified in FIG. 4 (and FIG. 5) by the reference number110.

FIG. 4 shows ring segments A1 and P1 curving down and away fromreference plane 110 as one proceeds to the left from a medial portion ofwhat is visible in FIG. 4. FIG. 4 also shows ring segments A3 and P3curving down and away from plane 110 as one proceeds to the right fromthe medial portion of FIG. 4.

Although points A1/P1 and A3/P3 are not per se visible in FIG. 4, theirapproximate left-right locations are indicated with arrows labeled A1/P1and A3/P3, respectively. It will be apparent from this depiction thatpoint A3/P3 is lower relative to plane 110 than point A1/P1. Thusdimension D3 (the distance of point A3/P3 below plane 110) is greaterthan dimension D1 (the distance of point A1/P1 below plane 110). Ring100 is thus asymmetrical from left to right (as viewed in FIG. 4) inthis respect.

FIG. 5 shows another view of ring 100 on an even larger scale than FIGS.3 and 4 (see FIG. 3 for the orientation of FIG. 5 relative to FIGS. 3and 4). FIG. 5 shows all the features of ring 100 that have beenpreviously described. FIG. 5 again shows that the side of ring 100 thatincludes point A3/P3 is displaced farther from plane 110 than the sideof the ring that includes point A1/P1. This is again shown in FIG. 5 bythe fact that dimension D3 is greater than dimension D1.

Note in connection with FIG. 5, especially, that the displacement atpoint A1/P1 from reference plane 110 is not necessarily the greatestdisplacement of that side of the ring from that plane. Another point(like 120 in FIG. 5) along P1 may actually have greater displacementfrom plane 110 than point A1/P1. The same may be true on the other sideof ring where point A3/P3 may not have that side's greatest displacementfrom plane 110. Another point 130 along P3 may have even greaterdisplacement from plane 110. Nevertheless, it remains the case thatpoint A3/P3 has greater displacement (D3) from plane 110 than pointA1/P1 has. Local maximum displacement point 130 (if different from pointA3/P3, as it is in ring 100) also has greater displacement from plane110 than local maximum displacement point 120 (again assumed to bedifferent than point A1/P1, as in ring 100). A possible embodiment isfor point A3/P3 to have greater displacement from plane 110 than anypoint (even point 120) on the other side of the ring.

It will also be noted from what has been shown and described about ring100 that, at a minimum, at least some portions of ring segments A3 andP3 curve, slope, or incline away from reference plane 110 (in thedirection away from ring segments A2 and P2) in order for point A3/P3 tobe displaced from that plane. Similarly, at least some portions of ringsegments A1 and P1 curve, slope, or incline away from plane 110 (in thedirection away from ring segments A2 and P2) in order for point A1/P1 tobe displaced from that plane. Both the A1/P1 side of the ring and theA3/P3 side of the ring are displaced to the same side of plane 110. Ring100 is thus saddle shaped. However, the displacement from plane 110 thatis reached on the A3/P3 side of the ring is greater than thedisplacement that is reached on the A1/P1 side of the ring. Theabove-mentioned saddle shape is thus somewhat asymmetrical, with theA3/P3 side of the ring being more depressed than the A1/P1 side of thering.

The greater “downward” displacement of the side of ring 100 thatincludes point A3/P3 is of significant benefit in compensating forpatient conditions like those described in the background section ofthis specification. Those conditions tend to downwardly displace tissuestructures 23 (and their associated structures 21) more than tissuestructures 25 (and their associated structures 21) (see again FIG. 2).Extra downward depression of the mitral valve annulus radially out fromleaflet segments A3 and P3 (and including posterior commissure 17) maybeneficially compensate for this problem. Such extra downward depressionof this portion of the valve annulus is provided by ring 100, which hasgreater displacement from plane 110 on its side that includes segmentsA3 and P3 and point A3/P3 than on its other side (i.e., its side thatincludes segments A1 and P1 and point A1/P1).

It is known that mitral valve annuloplasty prostheses are not alwayscomplete rings like ring 100. For example, a portion of the anteriorside of what would otherwise be a complete ring can be omitted toproduce a C-shaped prosthesis. Examples of such Cs are shown in FIGS. 6and 7. The C 200 in FIG. 6 has a relatively small gap 402 on theanterior side. The C 300 in FIG. 7 has a relatively large gap 402 on theanterior side. The anterior gap in FIG. 7 is approximately the maximumacceptable gap. Any amount of anterior-side gap (up to the approximateamount shown in FIG. 7) can be employed in C-shaped prostheses.

The present invention can be applied to C-shaped prostheses like thoseexemplified by FIGS. 6 and 7. The portions of such a C-shaped prosthesisthat are present in the C are shaped and disposed in three dimensions asthough they were the corresponding portions of a complete ring inaccordance with the invention (see also FIG. 8, which is another view ofillustrative C shown in FIG. 7). In other words, a C-shaped prosthesisin accordance with the invention is shaped as though made from acomplete ring in accordance with the invention, but with some of theanterior of the complete ring omitted to produce the C.

Although some portion of the anterior of a C in accordance with theinvention has been omitted, it is possible to visualize a “trajectory”of the anterior side. Chain-dotted line 400 indicates such a trajectoryin FIGS. 6-8. Note that trajectory 400 spans the entire anterior side ofeach C. Where the anterior side has structure or material (i.e., to theleft and right of anterior gap 402), trajectory 400 passes coaxially andcentrally along that structure. In gap 402 (where each C has no actualstructure or material) trajectory 400 continues smoothly out of thematerial to one side of the gap, across the gap, and into the materialon the other side of the gap. In other words, trajectory 402 follows thesame path that the anterior side of the prosthesis 200 or 300 would haveif it were a complete ring in accordance with the invention.

FIGS. 6 and 7 show that the same reference points R1 through R3 that aredescried above in connection with ring 100 can be used again to define areference plane 410 (see FIG. 8) that is useful in describing the shapeof Cs in accordance with the invention. In the case of such Cs, however,it is appropriate to say that reference points R1 and R2 are on anteriortrajectory 400. This is so because, depending on the size of gap 402,reference points R1 and R2 may be either in anterior material of the C(e.g., as in the case of FIG. 6) or in the anterior gap 402 (e.g., as inthe case of FIG. 7). The anterior trajectory concept makes it possibleto describe the locations of reference points R1 and R2 generically,regardless of the size of gap 402.

It is thus now possible to describe Cs in accordance with the invention(e.g., a C like 200 or 300) as including the following features: A1, P1,P2, P3, and A3 segments connected in series in that order; an anteriorgap 402; an anterior trajectory 400 as described above; ananterior-to-posterior axis AP perpendicular to and bisecting a linebetween reference points R1 and R2, both of which are located alonganterior trajectory 400; a greatest width dimension W measuredperpendicular to the AP axis, reference points R1 and R2 and the AP axisbeing located so that the AP axis bisects the greatest width dimension;each of reference points R1 and R2 being spaced from the AP axis by 0.5mm; reference point R3 on the posterior side of the C, spaced to oneside of the AP axis by 0.5 mm, and defining with reference points R1 andR2 a reference plane 410; both of points A1/P1 (where the A1 and P1segments meet) and A3/P3 (where the A3 and P3 segments meet) beingspaced from reference plane 410 to the same side of that plane; and thespacing of point A3/P3 from reference plane 410 being greater than thespacing of point A1/P1 from that plane. Other features that aredescribed above for complete rings in accordance with the invention areagain applicable to Cs in accordance with the invention because the onlysignificant difference between Cs and rings in accordance with theinvention is the omission of a portion of the anterior side of a ring toproduce a C. The therapeutic effects of Cs in accordance with theinvention are similar to the therapeutic effects described above forrings in accordance with the invention.

A wide range of materials are well known for making annuloplastyprostheses, and any of the known materials that are suitable for makingprostheses in accordance with this invention can be used. Examples ofsuitable materials include titanium, a titanium alloy, Elgiloy (acobalt-nickel alloy), Nitinol (a nickel-titanium alloy), stainlesssteel, a cobalt-chromium alloy, a ceramic, and a polymer (e.g.,ultra-high-molecular weight polyethylene, polyurethane, or the like).The prostheses of this invention (like ring 100 or Cs 200 or 300) canhave any desired degree of rigidity, consistent with the objective ofthis invention for the prosthesis to apply significant forces inparticular ways to various parts of the mitral valve annulus. Forexample, the prostheses of this invention can be rigid or substantiallyrigid. Alternatively, the prostheses of this invention may be capable ofsome plastic deformation if the surgeon wants to modify the prosthesisshape somewhat for a particular patient's anatomy. The prosthesis shouldnot be plastically deformable by the patient's anatomy alone, but theprosthesis may be capable of some elastic deformation in response to thepatient's anatomy, including changes in anatomical shapes as a result ofbody functions such as heartbeats. Nevertheless, a prosthesis that iscapable of such flexibility should always be resiliently trying toreturn to an unloaded shape like that shown in the FIGS. herein. In thatway, even a prosthesis that is capable of some flexibility is alwaysapplying the kind of therapeutic force to the mitral valve annulus thatis desired in accordance with the invention.

Just as any of several materials are suitable for use as the basicmaterial of the prostheses of this invention, the prostheses of thisinvention may also include other known annuloplasty prosthesis features.For example, the prostheses of this invention may be wrapped in orotherwise associated with fabric or other materials through whichsutures can be passed as part of the process of implanting theprosthesis in a patient.

It will be understood that the foregoing is only illustrative of theprinciples of the invention, and that various modifications can be madeby those skilled in the art. For example, certain aspects of theprosthesis shapes shown herein can be modified. As just one specificillustration of this, the ratio of greatest width to greatest height ofthe prosthesis (e.g., the horizontal and vertical dimensions,respectively, in FIG. 3) can be larger or smaller than what has beenspecifically shown.

1. A mitral valve annuloplasty ring having an anterior portion including A1, A2, and A3 segments, and a posterior portion including P1, P2, and P3 segments, the segments being connected in a closed loop series in the order A1, A2, A3, P3, P2, and P1, the ring having an AP axis that extends from the anterior portion to the posterior portion, a first reference point located on the anterior portion to one side of the AP axis, a second reference point located on the anterior portion to the other side of the AP axis, and a third reference point located on the posterior portion to one side of the AP axis, the AP axis being perpendicular to a line between the first and second reference points, and the first and second reference points and the AP axis being located so that the AP axis bisects a greatest width dimension of the ring that is measured perpendicular to the AP axis, each of the first through third reference points being spaced from the AP axis by 0.5 mm, and the first through third reference points lying in and thereby defining a reference plane, the ring further having a fourth reference point where the A1 and P1 segments meet, and a fifth reference point where the A3 and P3 segments meet, the fourth and fifth reference points being spaced from the reference plane to one side of that plane, and spacing of the fifth reference point from the reference plane being greater than spacing of the fourth reference point from the reference plane.
 2. The ring defined in claim 1 wherein the first and third reference points are both on the side of the AP axis that is closer to the fourth reference point.
 3. The ring defined in claim 1 wherein at least a portion of the P3 segment is spaced from the reference plane to the one side of the reference plane by an amount greater than the spacing of the fifth reference point from the reference plane.
 4. The ring defined in claim 3 wherein at least a portion of the P1 segment is spaced from the reference plane to the one side of the reference plane by an amount greater than the spacing of the fourth reference point from the reference plane.
 5. The ring defined in claim 4 wherein the spacing of the fifth reference point from the reference plane is greater than spacing of any portion of the P1 segment from the reference plane.
 6. A mitral valve annuloplasty prosthesis having a posterior portion including P1, P2, and P3 segments, and an anterior portion including A1 and A3 segments and a gap intermediate the A1 and A3 segments, the segments being connected in a series in the order A1, P1, P2, P3, and A3, the prosthesis having an AP axis that extends from the anterior portion to the posterior portion, a first reference point located to one side of the AP axis on a trajectory that includes a smooth continuation, across the gap, of both the A1 and A3 segments and that follows a path through the gap that would be occupied by material of the prosthesis if the prosthesis were a complete prosthetic ring, a second reference point located on the trajectory to the other side of the AP axis, and a third reference point located on the posterior portion to one side of the AP axis, the AP axis being perpendicular to a line between the first and second reference points, and the first and second reference points and the AP axis being located so that the AP axis bisects a greatest width dimension of the ring that is measured perpendicular to the AP axis, each of the first through third reference points being spaced from the AP axis by 0.5 mm, and the first through third reference points lying in and thereby defining a reference plane, the prosthesis further having a fourth reference point where the A1 and P1 segments meet, and a fifth reference point where the A3 and P3 segments meet, the fourth and fifth reference points being spaced from the reference plane to one side of that plane, and spacing of the fifth reference point from the reference plane being greater than spacing of the fourth reference point from the reference plane.
 7. The prosthesis defined in claim 6 wherein the first through third reference points are all located in material of the prosthesis.
 8. The prosthesis defined in claim 6 wherein the third reference point is located in material of the prosthesis and the first and second reference points are located in the gap.
 9. The prosthesis defined in claim 6 wherein the gap is located approximately centrally in the anterior portion.
 10. The prosthesis defined in claim 6 wherein the first and third reference points are both on the side of the AP axis that is closer to the fourth reference point.
 11. The prosthesis defined in claim 6 wherein at least a portion of the P3 segment is spaced from the reference plane to the one side of the reference plane by an amount greater than the spacing of the fifth reference point from the reference plane.
 12. The prosthesis defined in claim 11 wherein at least a portion of the P1 segment is spaced from the reference plane to the one side of the reference plan by an amount greater than the spacing of the fourth reference point from the reference plane.
 13. The prosthesis defined in claim 12 wherein the spacing of the fifth reference point from the reference plane is greater than spacing of any portion of the P1 segment from the reference plane.
 14. A method of treating a patient's mitral valve comprising: applying an annuloplasty prosthesis to the mitral valve adjacent the annulus of the mitral valve, the annuloplasty prosthesis dipping down adjacent the anterior and posterior valve commissures relative to at least some other portions of the annulus between the commissures, the prosthesis pushing down the portion of the annulus that is adjacent to the posterior commissure farther than the prosthesis dips down adjacent the anterior commissure.
 15. The method defined in claim 14 wherein the prosthesis comprises a ring.
 16. The method defined in claim 14 wherein the prosthesis is a C-shaped prosthesis having a gap adjacent at least a portion of the A2 segment of the valve leaflets.
 17. The method defined in claim 14 wherein the other portions of the annulus include at least a portion of the annulus that is adjacent the A2 segment of the valve leaflets and at least a portion of the annulus that is adjacent the P2 segment of the valve leaflets.
 18. The method defined in claim 15 wherein the ring also dips down adjacent at least a portion of each of the A1, A3, P1, and P3 segments of the valve leaflets relative to said portion of the annulus that is adjacent the A2 segment of the valve leaflets and said portion of the annulus that is adjacent the P2 segment of the valve leaflets. 